EROFS Adding Support For File-Backed Mounts To Benefit Containers & Sandboxes

The EROFS read-only file-system changes have been submitted now for ahead of the upcoming Linux 6.12 merge window. Notable this cycle is EROFS adding support for file-backed mounts.

EROFS is adding support for file-backed mounts so that file-system image files can be used directly without needing a loopback block device or similar. This file-backed mount support is intended for use with container images and sandboxes. Using file-backed mounts is intended to avoid loopback devices that can behave intricately and can simplify error-prone lifetime management of virtual block devices.

Alibaba's Gao Xiang explains of the EROFS file-backed mounts support:

"In this cycle, we'd like to add file-backed mount support, which has has been a strong requirement for years. It is especially useful when there are thousands of images running on the same host for containers and other sandbox use cases, unlike OS image use cases.

Without file-backed mounts, it's hard for container runtimes to manage and isolate so many unnecessary virtual block devices safely and efficiently, therefore file-backed mounts are highly preferred. For EROFS users, ComposeFS, containerd, and Android APEXes will directly benefit from it, and I've seen no risk in implementing it as a completely immutable filesystem."

In turn the experimental EROFS-over-fscache functionality has been deprecated. More details on the EROFS changes for Linux 6.12 via this pull request. The EROFS read-only file-system continues to prove popular for mobile devices as well as container-type use-cases.